Seawater alkalinity (AT), defined as a difference between the excess concentrations of proton acceptors over proton donors in 1 kg of seawater, is one of the important parameters in carbon dioxide systems. Due to its invariance during CO2 gas exchange and biological activity, AT is considered to be a cornerstone in analytical assessments of oceanic CO2 cycling. Anomalies of AT normalized to salinity have been contributed to water mass movement and/or dissolution of calcium carbonate.
Conventional systems and method for measuring seawater AT usually involve acid titration of the bases to carbonic acid end point by either a single step addition or sequential stepwise addition. The multi-step titration method is widely used on shipboard measurements due to its high precision and automated operation. The combined speed and simplicity of single-step titration with spectrophotometric pH determinations for measurement of end point excess acid has been shown. Such methods have greatly improved the precision of alkalinity measurements. However, these end point detections require accurate knowledge of end point pH without the influence of CO2 generated in titration steps and thus usually involve a purge step. Such step makes the automation of an online instrument difficult. The multipoint volumetric titration remains the standard procedure for discrete sampling.
Accordingly, what is needed in the art is an improved system and method for measuring the total alkalinity of a sample liquid which overcomes the limitations of the prior art systems.